First, lower the neck gaiter with your hands, being careful not to rub your nose and mouth until it is around your neck.
Then pull it out over your head like any other neck gaiter but with extra care. Prevent the neck gaiter from touching any area of your face while removing it.
Remove the filter and dispose of it immediately. Used filters should be disposed of in a closed container (e.g. plastic bag) and insulated to prevent contamination. Once you have removed the neck gaiter and the filter, avoid contact between the filter and your face or hands, to avoid contaminating yourself.
Wash your hands thoroughly with soap and water or disinfect them with antiseptic gel.
You can see how to do it step by step here.